Motion picture photographic films used in producing a release print (the film projected in movie theaters) include camera origination film, intermediate film, and the release print film. Current practice for most motion picture production involves the use of at least four photographic steps. The first step is the recording of the scene onto a camera negative photographic film. While the original negative (typically after editing) may be printed directly onto a negative working print film in a second step to produce a direct release print, most motion picture productions use an additional two intermediate steps. Typically, the original camera negative film is printed onto a negative working intermediate film, such as Eastman Color Intermediate Film, yielding a master positive. The master positive is subsequently printed again onto an intermediate film providing a duplicate negative. Finally, the duplicate negative is printed onto a print film forming the release print. In practice, several duplicate negative copies are produced from the master positive, and each of the duplicate negatives may then be used to make hundreds of print film copies. This multistep process helps save the integrity of the valuable original camera negative film in preparing multiple release prints. In certain situations, usually involving special effects, intermediate film may be used an additional two or more times in preparing the final duplicate negatives to be used in printing the release prints. In this case, the first duplicate negative is used to print onto intermediate film to produce a second master positive, which is in turn used to produce a second duplicate negative. The second duplicate negative may be then used for printing the release prints.
The wide variety of potential film products available for the above-mentioned processes can be produced on either of two commonly employed polymeric supports: cellulose triacetate (CTA) and polyethylene terephthalate (PET). It is becoming more common for specific film codes to be available on only one of these supports as opposed to either. Currently, acetate-based films, and the older, less common cellulose nitrate-based films, are spliced to themselves using film cements comprising organic solvents designed to partially solubilize the cellulose-based film supports. Satisfactory cement splicing requires careful scraping away of the emulsion layers of the lower film component prior to application of the film cement in order to allow intimate support contact. It is also important to allow sufficient clamping time in the splicer. Current recommendations are fifteen to thirty seconds under modest heat and pressure prior to handling of the splice. Because a cement splice does not attain fill strength for several hours, care is required when handling the film if immediate use is contemplated. Not only is this splicing technique cumbersome, time consuming, and a source of debris, but there are also health, safety and environmental concerns surrounding the components of the currently employed film cements.
With the advent of PET-based film products, a new splicing technique was required since this film support does not readily lend itself to cement splicing. The polymer used as the support base is not soluble in the solvents used in film cement and even more toxic solvents would be required to produce the same type of bonding with PET-based films. The most common method of splicing PET-based film, when it was originally introduced, was the use of pressure sensitive tapes. These tapes are costly, cumbersome, a potential source of dirt and require application to imaged frames adjacent to the splice itself.
A more convenient method of splicing PET-based films has been with the use of ultrasonic energy to essentially “weld” the two film members together. This splicing technique is typically accomplished in an overlap configuration, and within an area that will exclude perforations and/or an imaged frame. U.S. Pat. Nos. 3,574,037 and 4,029,538, and EP 0497 393, e.g., describe systems and apparatus employing the use of ultrasonic sealing devices that can be used to splice films, specifically motion picture films. These patents, however, refer only to the splicing or welding of polyester-based film products.
While the use of ultrasonic welding techniques has been suggested for splicing of acetate based film strips, attempts to do so have generally not been successful. Motion picture film splicers that have been developed which utilize ultrasonic energy to splice PET-based films together, e.g., when used to splice CTA-based films cause brittleness and diminished strength typically resulting in splices that are far too weak and/or rough for practical application. Such splices may exhibit levels of roughness that are likely to damage adjacent areas of film when wound in roll form. Additionally, the increased thickness produced by the molten acetate material may prevent splices from smooth conveyance through the tight tolerances encountered in film printing gates. Similarly, using existing ultrasonic splicing devices to join CTA and PET film stocks produces the same rough, distorted surface of the acetate film member. U.S. Pat. No. 3,700,532, e.g., notes some typical problems associated with attempts to ultrasonically splice acetate based film strips.
Japanese Kokais 57-072816 A and 57-073064 A describe materials that can be utilized to bond components using induction heating. These consist of thermoplastic resins coated on both sides of metallic films. These publications, however, refer only to the bonding media itself and not the adherends.
Japanese Kokai 55-119652 A teaches a method of splicing together photographic paper using induction heating. Overlapped sections of photographic paper webs are joined together by preheating the surfaces, prepressing and then induction heating under pressure to form a splice. This application relies on the thermal fusing of resin-coated paper to itself and not the bonding of photographic film products of differing polymeric composition.
Similarly there are numerous patent publications, among them Japanese Kokais 62-098307 A and 63-182610 A, that deal with the splicing together of optical fibers by means of induction heating. Again, the splice components are of homogeneous composition and the application is non-photographic.
There are also many patent publications, typified by Japanese Kokais 04-019139 A and 07-069369 A, that teach this technology for the use of lidding attachment in the bottling industry. The two patents referenced involve the use of an aluminum foil layer or similar electrically conducting support, coated on one surface with a thermoplastic resin layer having good adhesion to the container material.
There are numerous other patent publications that describe the use of 10 induction heating to bond various materials together. They range from bonding together shoe components (EP 0 919 151 A1), to the assembly of automotive panels (Japanese Kokai 59-076220 A), to the attachment of labels to metallic can bodies (Japanese Kokais 10-000683 A and 2001-047511 A).
To date no one has provided a method for successfully splicing together motion picture film strips composed of dissimilar polymeric supports that does not rely on the use of pressure-sensitive tape. The prior art has also failed to provide a method of splicing cellulosic-based motion picture film without the need for removal of the emulsion layer and application of a flammable and toxic solvent mixture.